So, Actor Formations are now a thing. You can have filled blocks of actors, open blocks (like this one), filled & open wedges, an open V formation, and filled or open diamonds. Position relative to group leader is arbitrary, and the formation may or may not include the leader. Circles are next.

EDIT: From what I can tell, it's just a filled rectangular block, so, yes. Although I do need to work out a lot more logic, especially for turning corners. My initial implementation just keeps everybody in the same places relative to the leader, but to be proper we need to be able to march forward and then turn ninety degrees by just having everybody turn and walk in the new direction, making one side the new front.

But then I get into the list of other things this needs - like more frequent think cycles so they stay closer to their formation position. The OpenSteer implementation reduces accuracy, but provides realism when they are changing positions, because they don't just run through each other. It would be pretty easy to make perfect formations by simply making everybody do exactly the same thing at the same time, but I kind of like the randomness here. If I can dial it down a bit it might come out acceptable.